The invention relates to a method for fabricating a patterned metal-oxide-containing layer. In particular, the invention relates to the fabrication of a patterned metal-oxide-containing layer which is used as a ferroelectric or paraelectric dielectric in a storage capacitor of a DRAM memory cell.
The dynamic semiconductor memory components (DRAMs) which are fabricated in microelectronics essentially comprise a selection or switching transistor and a storage capacitor in which a dielectric material is inserted between two capacitor plates. Usually, oxide or nitride layers having a dielectric constant of at most about 8 are mainly used as the dielectric. In order to reduce the size of the storage capacitor and to fabricate nonvolatile memories, xe2x80x9cnovelxe2x80x9d capacitor materials such as, for example, ferroelectric or paraelectric materials with significantly higher dielectric constants are required. Some of these materials are mentioned in the publication xe2x80x9cNeue Dielektrika fxc3xcr Gbit-Speicherchipsxe2x80x9d [New Dielectrics for Gbit Memory Chips] by W. Hxc3x6nlein, Phys. Bl. 55 (1999). In order to fabricate ferroelectric capacitors for applications in such nonvolatile semiconductor memory components having a high integration level, e.g. ferroelectric materials such as SrBi2 (Ta, Nb)2O3 (SBT or SBTN), Pb (Zr, Ti)O3 (PZT), or Bi4Ti3O12 (BTO) can be used as the dielectric between the capacitor plates. However, it is also possible to use a paraelectric material such as, for example, (BaSr) TiO3 (BST).
The use of these novel ferroelectric or paraelectric dielectrics presents new challenges to semiconductor process technology. This is because, firstly, these novel materials can no longer be combined with polysilicon, the traditional electrode material. Therefore, it is necessary to use inert electrode materials such as, for example, platinum-group metals, i.e. Pt, Pd, Ir, Rh, Ru or Os, or their conductive oxides (e.g. RuO2). It is also possible generally to use conductive oxides such as LaSrCoOx or SrRuO3. The reason for this is that after the deposition of the ferroelectric dielectric, the latter has to be thermally treated (xe2x80x9cconditionedxe2x80x9d) if appropriate a number of times in an oxygen-containing atmosphere at temperatures of about 550-800xc2x0 C. In order to avoid undesirable chemical reactions between the ferroelectric dielectric and the electrodes, the latter are therefore mainly produced from platinum or another sufficiently thermostable and inert material, such as another platinum-group metal or a conductive oxide.
During the fabrication of the storage capacitor, patterning steps are necessary in which the ferroelectric layer is partly removed by an etching step. In this case, it has been shown that the remaining edge regions of the ferroelectric layer are damaged in a certain way. In particular, it has been shown that the stoichiometric composition of SBT layers in the edge sections deviates from the original stoichiometric composition and has a deficiency of bismuth. SAMSUNG has disclosed a wet-chemical method in which the damaged regions around the storage capacitor produced from PZT material are removed after the etching step. However, this leads to an undesirable loss of layer material of the ferroelectric layer and thus to a loss of storage capacitance of the storage capacitor to be fabricated.
It is accordingly an object of the invention to provide a method of fabricating a patterned, metal-oxide-containing layer which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and in which damage to the metal-oxide-containing layer that has occurred during the patterning can be compensated without a loss of material.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of fabricating a patterned metal-oxide-containing layer. The method comprises the following method steps:
providing a substrate;
depositing a metal-oxide-containing layer on the substrate;
patterning the metal-oxide-containing layer and thereby causing edge sections of the metal-oxide-containing layer to have a stoichiometric deficiency of a given element in the metal-oxide-containing layer;
applying an annealing layer to cover the metal-oxide-containing layer at least on the edge sections, the annealing layer containing the given element of the metal-oxide-containing layer; and
heat-treating to diffuse the given element from the annealing layer into regions of the edge sections of the metal-oxide-containing layer having the stoichiometric deficiency.
In other words, a metal-oxide-containing layer is applied to the substrate; the metal-oxide-containing layer is patterned; an annealing layer is deposited, which covers the metal-oxide-containing layer at least on edge sections and which contains at least one element which is also contained in the metal-oxide-containing layer but, on account of the patterning, has a deficiency in the stoichiometric composition in the edge sections; and the assembly is subjected to a heat treatment in such a way that the element diffuses from the annealing layer into damaged regions of the edge sections of the metal-oxide-containing layer.
The method according to the invention can be carried out on a free-standing metal-oxide-containing layer, the annealing layer covering the metal-oxide-containing layer preferably completely, and thus in any case lying on the edge sections. However, it is also possible for a further layer to have been applied to the metal-oxide-containing layer before patterning and for both layers to have been patterned together, the annealing layer subsequently being applied to the further layer and the metal-oxide-containing layer in such a way that the annealing layer covers at least one lateral edge section of the metal-oxide-containing layer. In this case, the metal-oxide-containing layer may form the dielectric of a storage capacitor, the further layer may form the top electrode of the storage capacitor, and the substrate may be formed by the bottom electrode of the storage capacitor.
Afterwards, the annealing layer may be removed from the metal-oxide-containing layer and, if appropriate, the further layer. However, it may also be left on the metal-oxide-containing layer and, if appropriate, the further layer, in which case, however, it may be necessary to etch contact holes through the annealing layer for the purpose of making contact with the further layer. Particularly if the further layer is intended to serve as the top electrode of a storage capacitor, it may become necessary to form a contact hole through the annealing layer.
In accordance with an added feature of the invention, the heat treatment step is preferably performed in a temperature range of 500-800xc2x0 C., for a period of 5 to 30 min, and in an O2 or N2 atmosphere.
Preferably for the purpose of fabricating a storage capacitor for a DRAM memory cell, the metal-oxide-containing layer is formed by a ferroelectric or a paraelectric material. In the first-mentioned case, the metal-oxide-containing layer preferably contains one of the materials SrBi2 (Ta, Nb)2O9 (SBT or SBTN), Pb (Zr, Ti)O3 (PZT) or Bi4Ti3O12 (BTO). In the second-mentioned case, the metal-oxide-containing layer contains the material (BaSr) TiO3 (BST), for example. the metal-oxide-containing layer is formed by the material then the annealing layer may contain for example one or of the following materials: SBT, BiOx/SBT, SBT+BiOx, TiOx, BiTiOx/SBT, SBT/BiTiOx or BiOx.
The metal-oxide-containing layer and/or the annealing layer may be deposited by means of metal organic deposition (MOD), metal organic vapor-phase deposition (MOCVD) or by a puttering process.
For the case of fabricating a storage capacitor, a platinum-group metal or a conductive oxide of a platinum-group metal may be used as electrode material.
With the above and other objects in view there is also provided, in accordance with the invention, a method of fabricating a semiconductor component, such as a DRAM memory cell, which comprises:
forming a switching transistor on a semiconductor substrate;
depositing a first insulation layer on the switching transistor; and
forming a storage capacitor on the insulation layer, and thereby fabricating a dielectric of the storage capacitor by applying and patterning a metal-oxide-containing layer according to the above-outlined steps.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for fabricating a patterned metal-oxide-containing layer, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.